step 2: add thread safe state commands and cache model

README.md

@@ -2,7 +2,7 @@
 
 `dpg-map` is a Dear PyGui map widget package under rebuild.
 
-The Step 1 public API contract is in place:
+The Step 2 logical runtime model is in place:
 
 ```python
 import dpg_map as dpgm
@@ -13,14 +13,23 @@ provider = dpgm.TileProvider(
     attribution="Tiles (c) Example",
 )
 dpgm.register_provider(provider)
+
+with dpgm.map_widget(tag="map", center=(47.9029, 1.9093), zoom=15):
+    dpgm.add_marker("vehicle", lat=47.9029, lon=1.9093)
+
+dpgm.update_marker("vehicle", lat=47.9030, lon=1.9094, map_tag="map")
 ```
 
-Implemented in Step 1:
+Implemented so far:
 
 - public package exports
 - tile provider definitions and registry
 - Web Mercator projection helpers
-- initial cache dataclasses
-- explicit stubs for GUI-dependent public functions
+- thread-safe logical map state and map registry
+- command queue with coalescing for overlay and view updates
+- logical marker, polyline, trajectory, and layer models
+- persistent disk cache path, metadata, scanning, and prune planning
 
-GUI widget rendering and runtime state updates are planned for later rebuild steps.
+Dear PyGui rendering is not implemented yet. The current `map_widget` is a logical
+context manager used to register state; Step 3 will add the real child window,
+drawlist, sizing, and GUI-thread frame pump.